Turbo-electric turbo-compounding system

ABSTRACT

Exhaust gases (28) from an engine (16, 16′), input to turbo-compounder (20), drive a bladed turbine rotor (48) therein, which drives a generator (56, 56.1, 56.1′, 126, 126′, 126″), the output of which is used to electrically drive an induction motor (104, 104′), the rotor (106) of which is mechanically coupled to the engine (16, 16′) so as to provide for recovering power to the engine (16, 16′). The turbo-compounder (20) also incorporates a wastegate valve (36, 36′) to provide for the exhaust gases (28) to bypass the bladed turbine rotor (48). Upon startup the wastegate valve (36, 36′) is opened, and the generator may be decoupled from the engine (16, 16′). The generator (56, 56.1, 56.1′, 126, 126′, 126″) may be coupled to the engine (16, 16′) either by closure of a contactor (110, 110′), engagement of an electrically-controlled clutch (124), or by control of either a solid-state switching (125) or control system or an AC excitation signal (130), when the frequency (fGENERATOR) of the generator (56, 56.1, 56.1′, 126, 126′, 126″) meets or exceeds that (fMOTOR) of the induction motor (104, 104′). Wastegate valve (36, 36′) closure provides for the generator (56, 56.1, 56.1′, 126, 126′, 126″) to recover power from the exhaust gases (28).

CROSS-REFERENCE TO RELATED APPLICATIONS

The instant application claims the benefit of prior U.S. Provisional Application Ser. No. 62/111,208 filed on 3 Feb. 2015, which is incorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates a genset comprising a turbo-electric turbo-compounding system in cooperation with a diesel-electric generator system;

FIG. 2 illustrates a longitudinal-cross-sectional view of the turbo-compounder of the turbo-electric turbo-compounding system illustrated in FIG. 1;

FIG. 3 illustrates an isometric external view of the turbo-compounder illustrated in FIGS. 1 and 2;

FIG. 4 illustrates a wastegate valve incorporating a “belly-band” wastegate in cooperation with a plurality of orifices through a cylindrical wall of a cylindrical inlet duct;

FIG. 5 illustrates a cross-sectional view of the wastegate valve illustrated in FIG. 4;

FIG. 6 illustrates a block diagram of a genset incorporating a first aspect of a turbo-electric turbo-compounding system;

FIG. 7 illustrates a schematic block diagram of a three-phase generator operatively coupled to a three-phase induction motor through a contactor, in accordance with the first aspect of the turbo-electric turbo-compounding system illustrated in FIG. 6;

FIG. 8 illustrates a flow chart of a process for controlling the activation of the first aspect of the turbo-electric turbo-compounding system illustrated in FIGS. 1-7;

FIG. 9a illustrates a flow chart of a first embodiment of a process for controlling the deactivation of the first aspect of the turbo-electric turbo-compounding system illustrated in FIGS. 1-7;

FIG. 9b illustrates a flow chart of a second embodiment of a process for controlling the deactivation of the first aspect of the turbo-electric turbo-compounding system illustrated in FIGS. 1-7;

FIG. 10 illustrates a block diagram of a genset incorporating a second aspect of a turbo-electric turbo-compounding system;

FIG. 11 illustrates a flow chart of a process for controlling the activation of the second aspect of the turbo-electric turbo-compounding system illustrated in FIG. 10;

FIG. 12a illustrates a flow chart of a first embodiment of a process for controlling the deactivation of the second aspect of the turbo-electric turbo-compounding system illustrated in FIG. 10;

FIG. 12b illustrates a flow chart of a second embodiment of a process for controlling the deactivation of the second aspect of the turbo-electric turbo-compounding system illustrated in FIG. 10;

FIG. 13 illustrates a block diagram of a genset incorporating a third aspect of a turbo-electric turbo-compounding system;

FIG. 14 illustrates a block diagram of a genset incorporating a fourth aspect of a turbo-electric turbo-compounding system;

FIG. 15 illustrates a schematic block diagram of a three-phase asynchronous generator in cooperation with an associated induction generator inverter, operatively coupled to a three-phase induction motor, in accordance with the fourth aspect of the turbo-electric turbo-compounding system illustrated in FIG. 14;

FIG. 16 illustrates a schematic block diagram of a three-phase asynchronous generator operatively coupled to an associated induction generator inverter, in accordance with the fourth aspect of the turbo-electric turbo-compounding system illustrated in FIG. 14;

FIG. 17 illustrates a block diagram of one embodiment of an induction generator inverter;

FIG. 18 illustrates a graph of shaft torque as a function of rotational speed relative to the associated synchronous speed, for a generic induction motor operating in a motoring mode of operation;

FIG. 19 illustrates a graph of shaft torque as a function of rotational speed relative to the associated synchronous speed, for an induction machine over a range of rotational speeds spanning generating, motoring and braking modes of operation;

FIG. 20 illustrates a flow chart of a process for controlling the activation of a generic turbo-electric turbo-compounding system in accordance with any of the first through fourth aspects illustrated in FIG. 6, 10, 13 or 14;

FIG. 21a illustrates a flow chart of a first embodiment of a process for controlling the deactivation of a generic turbo-electric turbo-compounding system in accordance with any of the first through fourth aspects illustrated in FIG. 6, 10, 13 or 14; and

FIG. 21b illustrates a flow chart of a second embodiment of a process for controlling the deactivation of a generic turbo-electric turbo-compounding system in accordance with any of the first through fourth aspects illustrated in FIG. 6, 10, 13 or 14.

DESCRIPTION OF EMBODIMENT(S)

Referring to FIG. 1, a turbo-electric turbo-compounding system 10 cooperates with a genset 12 comprising a diesel-electric generator system 14, the latter of which comprises a genset engine 16, for example, a diesel engine 16′, operatively coupled to an associated genset main generator 18, wherein the main generator 18 is driven, i.e. rotated, by the crankshaft of the genset engine 16, 16′ and provides for generating electrical power for use external of the genset 12. Referring also to FIGS. 2-7, the turbo-electric turbo-compounding system 10 comprises a turbo-compounder 20 having an inlet 22 and an outlet 24 (wherein the relative left-right orientation of the inlet 22 and outlet 24 in FIGS. 2 and 3 is reversed relative to that shown in FIG. 1), the inlet 22 of which is operatively coupled to an exhaust discharge conduit 26 of the genset engine 16, 16′ and provides for receiving exhaust gases 28 therefrom into an associated inlet duct 30 that incorporates a plurality of orifices 32 through a cylindrical wall 34 thereof that constitute part of an associated wastegate valve 36 that provides for controlling whether or not exhaust gases 28 may flow therethrough.

For example, referring to FIGS. 4 and 5, a “belly-band” wastegate valve 36′ comprises a “belly-band” wastegate 37 in cooperation with the orificed portion of the cylindrical wall 34 of the inlet duct 30. The “belly-band” wastegate 37 comprises a flexible metallic band formed as a generally open-ended annular cylindrical shell surrounding the orifices 32 and the annular cylindrical wall 34 of the inlet duct 30. The “belly-band” wastegate 37 is axially-retained by a pair of associated radial guide flanges 38 that extend radially outward from the cylindrical wall 34, fore and aft of the “belly-band” wastegate 37. The radial guide flanges 38 incorporate a plurality of scalloped openings 39 from which the material of at least one radial guide flange 38 is removed. The ends 37.1, 37.2 of the “belly-band” wastegate 37 are coupled to a wastegate actuation mechanism 40, for example, a scissors-type wastegate actuation mechanism 40′, which is actuated by an associated linear wastegate valve actuator 41. When the wastegate valve actuator 41 is extended (as illustrated in FIG. 4, and as shown by the primary position illustrated in FIG. 5), the associated scissors-type wastegate actuation mechanism 40′ increases the effective diameter of the associated cylindrical shell formed by the “belly-band” wastegate 37, thereby creating an annular gap 42 between the outside of the cylindrical wall 34 of the inlet duct 30 and the inside of the “belly-band” wastegate 37, through which exhaust gases 28 may flow, and from which the exhaust gases 28 may be discharged from the “belly-band” wastegate valve 36′ via the associated scalloped openings 39. When the wastegate valve actuator 41 is contracted (as shown by the alternative position illustrated in FIG. 5), the associated scissors-type wastegate actuation mechanism 40′ reduces the effective diameter of the associated cylindrical shell of the “belly-band” wastegate 37, until, when fully contracted, the “belly-band” wastegate 37 is constricted tightly around the cylindrical wall 34 of the inlet duct 30, thereby blocking each of the orifices 32, so as to block a flow of exhaust gases 28 therethrough.

Alternatively, the wastegate valve 36 could be implemented with a wastegate band incorporating a plurality of second orifices that are similar in number to the plurality of orifices 32, wherein the wastegate band is then rotationally positioned relative to the cylindrical wall 34 by an associated wastegate actuation mechanism 40 to control the relative alignment of the orifices 32 in the cylindrical wall 34 with the corresponding second plurality of orifices, thereby controlling the effective opening area of the associated wastegate valve 36, which can range from fully closed with all of the orifices 32 blocked by corresponding non-orificed portions of the wastegate band, to fully open with all of the orifices 32 aligned with corresponding second orifices of the wastegate band.

With the wastegate valve 36 closed, nominally all of the exhaust gases 28.1 entering the inlet 22 of the turbo-compounder 20 are directed axially through the inlet duct 30, and upon exit therefrom, flow through an associated turbine nozzle 44 comprising a plurality of vanes 46 upstream of an associated bladed turbine rotor 48. The inlet side 44.1 of the turbine nozzle 44 incorporates a domed shroud 50 that provides for guiding the portion of exhaust gases 28 impinging thereon, onto the vanes 46 and through the openings therebetween of the turbine nozzle 44. The exhaust gases 28.2 exiting the turbine nozzle 44 then impinge upon the blades 48.1 of the bladed turbine rotor 48, causing a rotation thereof responsive thereto. The bladed turbine rotor 48 is operatively coupled by a rotor shaft 52 to the rotor 54 of a synchronous AC generator 56, for example, with the rotor shaft 52 splined to the bladed turbine rotor 48 so as to provide for the transmission of torque from the bladed turbine rotor 48 to the rotor shaft 52 of the synchronous AC generator 56. For example, in one set of embodiments, the synchronous AC generator 56 comprises a permanent magnet AC generator 56.1, for example, a three-phase permanent magnet AC generator 56.1′ (for example, of radial-flux design), or more generally, a multi-phase permanent magnet AC generator comprising at least three phases.

Electrical power, for example, three-phase AC power, is extracted from the synchronous AC generator 56 by an associated set of stator windings 58 that are relatively fixed with respected to an associated core housing structure 60 that is supported, for example, via a plurality struts 62, from within and by a housing duct 64 of the turbo-compounder 20. Accordingly, a rotation of the bladed turbine rotor 48 responsive to an interaction with the exhaust gases 28.2 exiting the turbine nozzle 44 causes a rotation of the rotor 54 of the synchronous AC generator 56 relative to the stator windings 58 thereof, which causes the generation of AC power from the stator windings 58. The exhaust gases 28.3 exiting the bladed turbine rotor 48 following the interaction therewith are discharged through an annular exhaust duct 66 that surrounds the core housing structure 60 at a forward end portion 60.1 thereof, wherein an outer shell 68 of the annular exhaust duct 66 depends from the core housing structure 60 via a plurality of associated struts 70 therebetween, wherein a turbine shroud 72 surrounding the bladed turbine rotor 48 extends forward from the outer shell 68 of the annular exhaust duct 66. The exhaust gases 28.4 exiting the annular exhaust duct 66 are discharged into an annular plenum 74 surrounding the core housing structure 60 and in fluid communication both with the outlet 24 of the turbo-compounder 20 and with the exterior of the “belly-band” cylindrical wastegate 37 of the wastegate valve 36.

With the wastegate valve 36 open, exhaust gases 28.1 entering the inlet 22 of the turbo-compounder 20 are able to flow radially through the orifices 32 and into the annular gap 42 of the wastegate valve 36, through the scalloped openings 39 of the associated radial guide flanges 38, and then directly into the annular plenum 74, thereby bypassing the bladed turbine rotor 48 which would not be affected thereby, and which otherwise extracts power from the exhaust gases 28, 28.2, 28.3 flowing thereacross.

The synchronous AC generator 56 is located within an open-ended cavity 76 in the core housing structure 60, the aft end portion 60.2 of which is closed by an end cap 78 secured thereto. A forward portion 52.1 of the rotor shaft 52 is rotationally supported from within the forward end portion 60.1 of the core housing structure 60 by a sleeve bearing 80 depending therefrom, and an aft portion 52.2 of the rotor shaft 52 is rotationally supported from the end cap 78 by a rolling element bearing 82, wherein the rotor shaft 52 is sealed with respect to the core housing structure 60 at locations between the synchronous AC generator 56 and each of the sleeve 80 and rolling element 82 bearings by corresponding respective forward 84.1 and aft 84.2 seals. The core housing structure 60 incorporates an annular coolant cavity 86 in fluid communication with coolant inlet 88 and outlet 90 ports that extend within and through corresponding struts 62 and the housing duct 64, wherein coolant admitted to the coolant inlet port 88 flows into and through the annular coolant cavity 86 and out of the coolant outlet port 90, so as to provide for cooling the synchronous AC generator 56 and the associated sleeve 80 and rolling element 82 bearings from the heat of the exhaust gases 28, and from the operation thereof. The core housing structure 60 also incorporates internal lubrication channels and cavities that provide for the lubrication of the sleeve 80 and rolling element 82 bearings, which are in fluid communication with corresponding ports extending within and through corresponding struts 62 and the housing duct 64 that provide for a respective source and sink of lubricant thereto and therefrom. The outside of a forward extension 30.1 of the inlet duct 30 is sealed to the inside of the housing duct 64 with one or more piston ring seals 92 that provide for translation of the inlet duct 30 relative to the housing duct 64 responsive to thermally-induced expansion and contractions of the associated components.

Referring to FIG. 3, in accordance with one embodiment, the opening position of the wastegate valve 36 is controlled by a pneumatic wastegate-valve actuator 41 of the wastegate actuation mechanism 40 responsive to a pneumatic actuation signal 96 from an electrically-controlled three-way valve 98, responsive to an associated wastegate control signal 99. The pneumatic wastegate-valve actuator 41′ incorporates a spring-biased diaphragm that is operatively coupled to the “belly-band” wastegate valve 36 so as to provide for positioning the associated “belly-band” wastegate 37 relative to the inlet duct 30 responsive to the displacement of the diaphragm, the latter of which is responsive to a pressure differential thereacross, wherein spring bias acts to bias the “belly-band” wastegate 37 so that the associated “belly-band” wastegate valve 36 is fully open, one side of the diaphragm is vented to the atmosphere 100, and the pressure on the other side of the diaphragm is controlled by the pneumatic actuation signal 96. With the electrically-controlled three-way valve 98 fully ON, the pneumatic actuation signal 96 is provided by a turbocharger boost pressure 102 from a turbocharger of the genset engine 16, 16′, which causes the wastegate valve 36 to become fully closed; and with the electrically-controlled three-way valve 98 fully OFF, the pneumatic actuation signal 96 is vented to the atmosphere 100, so as to provide for the wastegate valve 36 to become fully open responsive to the associated spring bias. Alternatively, the pneumatic wastegate-valve actuator 41′ could be configured so as to be responsive to vacuum rather than positive gage pressure. Further alternatively, the wastegate actuation mechanism 40 could be controlled with other types of actuators, for example, electro-mechanical or hydraulic. The collective effective opening area of the orifices 32 and scalloped openings 39 of the wastegate valve 36 is configured so as to provide for sufficient flow therethrough under no-load conditions when the wastegate valve 36 is open, for example, sufficient so that the resulting rotational speed of the synchronous AC generator 56, 56.1, 56.1′ does not exceed a safe operating threshold, or to prevent an over-speed of the bladed turbine rotor 48, either during startup of the turbo-electric turbo-compounding system 10, or when the associated electrical load is either absent or removed therefrom, either during normal operation or as a result of a failure scenario.

Referring to FIGS. 1, 6 and 7, the synchronous AC generator 56, 56.1, 56.1′ of the turbo-compounder 20 is used to drive an induction motor 104, with the rotor 106 of the induction motor 104 mechanically coupled to the crankshaft of the genset engine 16, 16′, for example, through a gearbox 108, (designated as G/B in FIG. 6), so as to provide for the induction motor 104 to supply mechanical shaft power to the genset engine 16, 16′. Accordingly, the turbo-compounder 20 provides for recovering power from the exhaust gases 28 of the genset engine 16, 16′ by first using the synchronous AC generator 56, 56.1, 56.1′ to convert fluid power of the exhaust gases 28 to AC electrical power, and then using the induction motor 104 to convert that AC electrical power to mechanical shaft power, which can be used to either supplement the mechanical shaft power of the genset engine 16, 16′ to drive the associated genset main generator 18, or which could be used separately.

In accordance with a first aspect of the turbo-electric turbo-compounding system 10, 10.1—illustrated in FIGS. 1, 6 and 7—the synchronous AC generator 56, 56.1, 56.1′ is directly connected to the induction motor 104 via an associated contactor 110, the latter of which is under control of a controller 112. More particularly, each phase A, B, C of a three-phase permanent magnet AC generator 56.1′ is directly connected to a corresponding phase A, B, C of a corresponding three-phase induction motor 104′ via a corresponding respective contact 110 ^(A), 110 ^(B), 110 ^(C) of an associated three-pole contactor 110′, or more generally, a multi-phase induction motor and an associated multi-phase contactor, comprising at least three phases, wherein the number of phases is the same as the number of phases of the associated multi-phase permanent magnet AC generator.

A permanent magnet AC generator 56.1, 56.1′ produces an output that is characterized by a relatively fixed relationship between output voltage and frequency—i.e. to the first order without loading and temperature effects, output voltage increases linearly with frequency, copasetic for driving induction motors—and accordingly provides for running the induction motor 104, 104′ directly. Accordingly, when directly connected thereto, the permanent magnet AC generator 56.1, 56.1′ is a synchronous machine that provides a synchronous frequency directly to the induction motor 104, 104′. Alternatively, the synchronous AC generator 56 could be implemented as a field-controlled synchronous AC generator.

The synchronous AC generator 56, 56.1, 56.1′ incorporates a first rotational-speed or frequency sensor 114, for example, a corresponding separate rotational-speed-sensing winding 114′ that provides for sensing the rotational speed thereof. Similarly, the induction motor 104, 104′ also incorporates a second rotational-speed or frequency sensor 116, for example, a corresponding separate rotational-speed-sensing winding 116′ that provides for sensing the rotational speed thereof. The first 114 and second 116 rotational speed or frequency sensors are operatively coupled to the controller 112, which provides for controlling the wastegate valve 36 and contactor 110, 110′ responsive to the respective first 118 and second 120 rotational-speed or frequency signals respectively generated therefrom. More particularly, the controller 112 generates both the wastegate control signal 99 for controlling the wastegate valve 36 and a contactor control signal 121 for controlling the contactor 110, 110′, responsive to the first 118 and second 120 rotational-speed or frequency signals, and, as described more fully hereinbelow, alternatively, also responsive to a phase-current signal 122 representative of the phase current I_(PHASE) supplied by the synchronous AC generator 56, 56.1, 56.1′ to the induction motor 104, 104′, for one of the associated phases A, B, C.

For example, either or both the first 114 or second 116 rotational speed or frequency sensor could be implemented with rotational-speed sensor attached to the corresponding shaft of the synchronous AC generator 56, 56.1, 56.1′ or induction motor 104, 104′. For example, such a rotational-speed sensor could incorporate either magnetic or optical sensing technology, for example, but not limited to, using either a magnetic pickup in cooperation with a toothed wheel, a resolver, a synchro, an optical encoder or a photodetector in cooperation with a shaft-associated reflector. The rotational-speed sensor generates a corresponding first 118 or second 120 rotational-speed or frequency signal responsive to the associated rotational speed of the shaft being sensed, either in the form of a speed measurement or an associated AC signal having a frequency dependent upon both the rotational speed of the corresponding associated shaft and the associated effective pole count of the rotational-speed sensor, i.e. the number of cycles of the resulting associated signal from the rotational-speed sensor per rotation of the associated shaft being sensed. Alternatively, either the first 114 or second 116 rotational speed or frequency sensor could be implemented with a corresponding first 114′ or second 116′ rotational-speed-sensing winding as either a corresponding associated separate isolated stator winding, or as one or more of the corresponding associated stator windings of the phases A, B, C of the synchronous AC generator 56, 56.1, 56.1′ or induction motor 104, 104′, respectively.

Referring to FIG. 8, in accordance with a startup process 800 for controlling the startup of a genset 12 incorporating the first aspect of the turbo-electric turbo-compounding system 10, 10.1, in step (802), the wastegate valve 36 is initially open—i.e. with the electrically-controlled three-way valve 98 positioned so that the pneumatic actuation signal 96 acting on the pneumatic wastegate-valve actuator 41′ is vented to atmosphere 100—so as to provide for the exhaust gases 28 to flow relatively unimpeded through the turbo-compounder 20 without acting upon the bladed turbine rotor 48. In step (804), the contactor 110, 110′ is also initially open, so as to prevent electrical power from being extracted from the synchronous AC generator 56, 56.1, 56.1′. As a result, the exhaust gases 28, 28.1, 28.2 can flow through the turbine nozzle 44 and across the bladed turbine rotor 48 without substantial loss. Accordingly, following step (804), the exhaust gases 28 flowing through the turbo-compounder 20 will either bypass the bladed turbine rotor 48 or flow thereacross without causing the generation of electrical power from the synchronous AC generator 56, 56.1, 56.1′, so as to provide for minimum back pressure in the exhaust discharge conduit 26, and thereby not impede a startup of the genset engine 16, 16′—if not already running. Then, in step (806), if not already started, the genset engine 16, 16′ is started; and, if not already running at rated speed, the genset engine 16, 16′ is run at rated speed, so as to provide for the generation of electrical power by the genset main generator 18. Then, in step (808), the wastegate valve 36 is fully closed by positioning the electrically-controlled three-way valve 98 so that the pneumatic actuation signal 96 acting on the pneumatic wastegate-valve actuator 41′ is provided by the turbocharger boost pressure 102, which causes substantially all of the exhaust gases 28.1 entering the inlet 22 of the turbo-compounder 20 to flow through the turbine nozzle 44 and across the bladed turbine rotor 48, thereby causing rotational acceleration of the bladed turbine rotor 48. Meanwhile, with the genset engine 16, 16′ running at rated speed following step (806), the rotor 106 of the induction motor 104, 104′ will be driven by the genset engine 16, 16′ through the associated gearbox 108 at a corresponding rated rotational speed, the latter of which is sensed by the associated second rotational-speed or frequency sensor 116, with the value of the associated resulting second rotational-speed or frequency signal 120 being designated f_(MOTOR).

The output frequency of the synchronous AC generator 56, 56.1, 56.1′ is directly proportional to the rotational speed thereof, and the waveform of the generated voltage is, by definition, synchronized with the rotational position of the synchronous AC generator 56, 56.1, 56.1′. The induction motor 104, 104′ will act as a load on the synchronous AC generator 56, 56.1, 56.1′ when operated at a rotational speed for which the corresponding associated synchronous frequency is less than the output frequency of the synchronous AC generator 56, 56.1, 56.1′ by a frequency difference, referred to as “frequency slip”, wherein the magnitude of the frequency slip increases with load as necessary to generate the required torque in the rotor shaft 52 driving the synchronous AC generator 56, 56.1, 56.1′. Under no-load conditions, frequency slip will be nearly zero, but non-zero as a result of parasitic losses, friction, and windage in the induction motor 104, 104′. Under no-load conditions, the ratio of the rotational speeds of the induction motor 104, 104′ and the synchronous AC generator 56, 56.1, 56.1′ is governed by the ratio of the number of poles of the respective electrical machines, with both the induction motor 104, 104′ and the synchronous AC generator 56 operating at nearly the same frequency, wherein the frequency of the excitation signal generated by the synchronous AC generator 56, 56.1, 56.1′ would differ from the corresponding rotational frequency of the induction motor 104, 104′ because of slip inherent in the operation of the induction motor 104, 104′. Accordingly, the ratio of the number of poles of the synchronous AC generator 56, 56.1, 56.1′ to the number of poles of the induction motor 104, 104′ provides for a substantial reduction of the speed of the induction motor 104, 104′ relative to that of the synchronous AC generator 56, 56.1, 56.1′, so as to provide for then mechanically interfacing the induction motor 104, 104′ with the genset engine 16, 16′ in order to provide for recovering power from exhaust flowing through the turbo-compounder 20 as mechanical shaft power to the genset engine 16, 16.

In step (810), the rotational speed, or corresponding output frequency, of the synchronous AC generator 56, 56.1, 56.1′ is sensed by the associated first rotational speed or frequency sensor 114 so as to generate a corresponding first rotational-speed or frequency signal 118—designated as f_(GENERATOR)—, which is compared with the corresponding second rotational-speed or frequency signal 120, i.e. f_(MOTOR), associated with the induction motor 104, 104′. If, in step (812), the rotational speed, or corresponding frequency f_(GENERATOR) of the synchronous AC generator 56, 56.1, 56.1′ is greater than or equal to the corresponding rotational speed, or corresponding frequency f_(MOTOR) of the induction motor 104, 104′—indicative of a prospective positive “frequency slip” condition—then, in step (814), the contactor 110, 110′ is closed, so as to directly electrically connect the synchronous AC generator 56, 56.1, 56.1′ to the induction motor 104, 104′. Otherwise, the process repeats with step (810) until the condition of step (812) is satisfied. More particularly, for a three-phase system, in step (814), each of the contacts 110 ^(A), 110 ^(B), 110 ^(C) of the three-pole contactor 110′ is closed so as to connect each of the phases A, B, C of the three-phase permanent magnet AC generator 56.1′ to corresponding respective phases A, B, C of the three-phase induction motor 104′. The closing of the contactor 110, 110′ at or near the point at which the frequencies of the synchronous AC generator 56 and the induction motor 104, 104′ are equal results in associated contact closure at near zero phase current. Following the connection of the phases A, B, C of the three-phase permanent magnet AC generator 56.1′ to corresponding phases A, B, C of the three-phase induction motor 104′, the rotational speed of the synchronous AC generator 56, 56.1, 56.1′ will continue to increase, resulting in a corresponding increase in “frequency slip”, which causes the synchronous AC generator 56, 56.1, 56.1′ to generate and transfer power to the three-phase induction motor 104′, which in turn results in an increase in the torque demand by the synchronous AC generator 56, 56.1, 56.1′, which increases the torque in the rotor shaft 52 between the bladed turbine rotor 48 and the rotor 54 of the synchronous AC generator 56, 56.1, 56.1′, which acts to reduce the acceleration, or decelerate, the bladed turbine rotor 48, until an equilibrium is reached for which the “frequency slip” and associated torque in the rotor shaft 52 corresponds to the level of power delivered to the induction motor 104, 104′ from the synchronous AC generator 56, 56.1, 56.1′, the latter of which results in an associated recovery of mechanical shaft power by the genset engine 16, 16′ responsive to a torque from the rotor 106 of the induction motor 104 acting on the genset engine 16, 16′ via the associated gearbox 108, at the rotational speed of the genset engine 16, 16′.

The controller 112 is designed to change the switching state of the contactor 110, 110′ when synchronous AC generator 56, 56.1, 56.1′ is synchronized, or nearly synchronized, with the induction motor 104, 104′ in respect of the associated operating frequencies. Although an inadvertent closure, or opening, of the contactor 110, 110′, for example, as a result of a failure mode, when the synchronous AC generator 56, 56.1, 56.1′ is not synchronized with the induction motor 104, 104′ will cause arcing in proportion to the magnitude of the associated speed or frequency differential, the contacts 110 ^(A), 110 ^(B), 110 ^(C) of the contactor 110, 110′ would be designed to accommodate such occurrences provided these occurrences are infrequent.

Accordingly, the turbo-electric turbo-compounding system 10, 10.1 is self-regulating because as the torque provided by the induction motor 104, 104′ to the genset engine 16, 16′ increases, the associated phase current in the induction motor 104, 104′ increases, which in turn increasingly loads the synchronous AC generator 56, 56.1, 56.1′, causing an increase in the torque demand on the bladed turbine rotor 48, which in turn results in a decrease of the rotational speed of the bladed turbine rotor 48 and synchronous AC generator 56, 56.1, 56.1′, which in turn results in a decrease of the torque provided by the induction motor 104, 104′ to the genset engine 16, 16′. At each operating condition there should be a stable point where the “frequency slip” results in a load condition of the genset engine 16, 16′ which is stable and for which the shaft torque of the genset engine 16, 16′ is reduced by some percentage, which in turn decreases fuel consumption by the genset engine 16, 16′ as a result of energy recovery from waste heat in the exhaust gases 28 therefrom, resulting in a reduction in the temperature of the exhaust gases 28.5 at the outlet 24 of the turbo-compounder 20 relative to that at the inlet 22, for example, as illustrated in FIG. 2.

The genset engine 16, 16′ may be shut down without first decoupling the turbo-electric turbo-compounding system 10, 10.1 from the genset engine 16, 16′—i.e. by opening both the wastegate valve 36 and the contactor 110, 110′, —provided that the wastegate valve 36 and contactor 110, 110′ are both opened prior to the next startup.

Alternatively, referring to FIGS. 9a and 9b , the turbo-electric turbo-compounding system 10, 10.1 may be disabled without first shutting down the genset engine 16, 16′. Referring to FIG. 9a in accordance with a first embodiment of a shutdown process 900 for decoupling the first aspect of the turbo-electric turbo-compounding system 10, 10.1, from step (902), with the genset engine 16, 16′ running and both the wastegate valve 36 and the contactor 110, 110′ closed, in step (904), the wastegate valve 36 is opened so as to prevent a subsequent overspeed of the bladed turbine rotor 48 upon removal of the associated electrical load from the synchronous AC generator 56, 56.1, 56.1′. As a result, the exhaust gases 28 are bypassed around the bladed turbine rotor 48, the latter of which then decelerates from a rotational speed for which the associated frequency of the f_(GENERATOR) of the synchronous AC generator 56, 56.1, 56.1′ was in excess of the frequency f_(MOTOR), of the induction motor 104, 104′ by an initial level of “frequency slip”. In step (906), the rotational speed, or corresponding output frequency f_(GENERATOR), of the synchronous AC generator 56, 56.1, 56.1′ sensed by the associated first rotational speed or frequency sensor 114 is compared with the rotational speed, or corresponding frequency f_(MOTOR), of the induction motor 104, 104′ sensed by the associated second rotational speed or frequency sensor 116. If, in step (908), the rotational speed, or corresponding output frequency f_(GENERATOR) of the synchronous AC generator 56, 56.1, 56.1′ is less than or equal to the corresponding rotational speed, or corresponding frequency f_(MOTOR) of the induction motor 104, 104′—indicative of negligible associated phase current—then, in step (910), the contactor 110, 110′ is opened so as to disconnect the synchronous AC generator 56, 56.1, 56.1′ from the induction motor 104, 104′. Otherwise, the process repeats with step (906) until the condition of step (908) is satisfied.

The changing of the state of the contactor 110, 110′ in steps (814) and (910) when the frequencies f_(GENERATOR), f_(MOTOR) of the synchronous AC generator 56, 56.1, 56.1′ and induction motor 104, 104′ are equal or nearly equal provides for switching at zero or nearly zero associated phase current, which provides for improving the reliability of the associated contacts 110 ^(A), 110 ^(B), 110 ^(C) of the contactor 110, 110′.

Alternatively, referring to FIG. 9b , a second embodiment of a shutdown process 900′ for decoupling the first aspect of the turbo-electric turbo-compounding system 10, 10.1 is the same as the above-described first embodiment of the shutdown process 900 except that steps (906) and (908) of the first embodiment 900 are respectively replaced with steps (912) and (914) of the second embodiment 900′, the latter which provide for determining when to open the contactor 110, 110′ explicitly responsive to a measurement—from an associated phase current sensor 123—of phase current I_(PHASE) from the synchronous AC generator 56, 56.1, 56.1′ to the induction motor 104, 104′ for one of the corresponding phases A, B, C. For example, the phase current sensor 123 may either incorporate, or be implemented with, a current transformer 123′. More particularly, following above-described step (904), in step (912) the phase current I_(PHASE) from the synchronous AC generator 56, 56.1, 56.1′ to the induction motor 104, 104′ of one of the phases A, B or C is explicitly measured by the phase current sensor 123 with the contactor 110, 110′ closed. Then, in step (914), if the phase current I_(PHASE) is less than a threshold, then, in step (910), the contactor 110, 110′ is opened. Otherwise, the process repeats with step (912) until the condition of step (914) is satisfied. Accordingly, the second embodiment of the shutdown process 900′ explicitly provides for opening the contactor 110, 110′ at a zero or near-zero current condition, which provides for minimizing arcing across the contacts 110 ^(A), 110 ^(B), 110 ^(C) of the contactor 110, 110′.

Referring to FIG. 10, in accordance with a second aspect of the turbo-electric turbo-compounding system 10, 10.2, the synchronous AC generator 56, 56.1, 56.1′ is directly connected to the induction motor 104, 104′, the latter of which is operatively connected to the gearbox 108 via an electrically-controlled clutch 124, which, when activated responsive to an clutch-control signal 124′ generated by the controller 112, provides for a transmission of torque from the rotor 106 of the induction motor 104 to the gearbox 108; and when deactivated, provides for the rotor 106 of the induction motor 104 to be decoupled from the gearbox 108, and therefore decoupled from the genset engine 16, 16′. More particularly, with the synchronous AC generator 56, 56.1, 56.1′ directly connected to the induction motor 104, 104′, each phase A, B, C of the three-phase permanent magnet AC generator 56.1′ is directly connected to a corresponding phase A, B, C of the three-phase induction motor 104′. The electrically-controlled clutch 124 provides for controlling whether or not the induction motor 104, 104′ is coupled to the genset engine 16, 16′, and therefore, whether or not the induction motor 104, 104′ is capable of consuming a substantial amount of power from the three-phase permanent magnet AC generator 56.1′. Accordingly, the electrically-controlled clutch 124 provides for effectively controlling whether or not a substantial amount of power can be transferred from the synchronous AC generator 56, 56.1, 56.1′ to the induction motor 104, 104′, just as the contactor 110, 110′ had provided for in the context of the first aspect of the turbo-electric turbo-compounding system 10, 10.1.

More particularly, referring to FIG. 11, in accordance with a startup process 1100 for controlling the startup of a genset 12 incorporating the second aspect of the turbo-electric turbo-compounding system 10, 10.2, in step (1102), the wastegate valve 36 is initially open so as to provide for the exhaust gases 28 to flow relatively unimpeded through the turbo-compounder 20 without acting upon the bladed turbine rotor 48. In step (1104), the electrically-controlled clutch 124 is deactivated, so as to prevent a mechanical loading of the induction motor 104, 104′, which thereby prevents a more than insubstantial amount of electrical power from being extracted from the synchronous AC generator 56, 56.1, 56.1′. As a result, the exhaust gases 28, 28.1, 28.2 can flow through the turbo-compounder 20 without a substantial loss of energy. Accordingly, following step (1104), the exhaust gases 28 flowing through the turbo-electric turbo-compounding system 10, 10.2 will either bypass the bladed turbine rotor 48 or flow thereacross without causing a substantial electrical load on the synchronous AC generator 56, 56.1, 56.1′, so as to provide for minimum back pressure in the exhaust discharge conduit 26, and thereby not impede a startup of the genset engine 16, 16′, if the genset engine 16, 16′ is not already running. Then, in step (1106), if not already started, the genset engine 16, 16′ is started; and, if not already running at rated speed, the genset engine 16, 16′ is run at rated speed, so as to provide for the generation of electrical power by the genset main generator 18. With the electrically-controlled clutch 124 initially deactivated following step (1104), if the genset engine 16, 16′ is started in step (1106), then the induction motor 104, 104′ will initially be stationary, or nearly so depending upon the extent to which exhaust gases 28.2 exiting the turbine nozzle 44 cause a rotation of the bladed turbine rotor 48, notwithstanding the wastegate valve 36 being open.

In step (1108), the first rotational-speed or frequency signal 118 of the synchronous AC generator 56, 56.1, 56.1′, sensed by the associated first rotational speed or frequency sensor 114, is compared with the corresponding second rotational-speed or frequency signal 120 associated with the induction motor 104, 104′. If, in step (1110), the rotational speed, or corresponding frequency f_(GENERATOR) of the synchronous AC generator 56, 56.1, 56.1′ is greater than or equal to the corresponding rotational speed, or corresponding frequency f_(MOTOR) of the induction motor 104, 104′—indicative of a prospective positive “frequency slip” condition—then, in step (1112), the electrically-controlled clutch 124 is activated, so as to provide for the induction motor 104, 104′—already directly electrically connected the synchronous AC generator 56, 56.1, 56.1′—to load the synchronous AC generator 56, 56.1, 56.1′, which in turn, loads the bladed turbine rotor 48, initially causing a rotational deceleration thereof if rotating. Then, in step (1114), the wastegate valve 36 is closed fully, which causes substantially all of the exhaust gases 28.1 entering the inlet 22 of the turbo-compounder 20 to flow through the turbine nozzle 44 and across the bladed turbine rotor 48, thereby causing rotational acceleration of the bladed turbine rotor 48, so as to provide for the latter to reach an equilibrium speed for which the “frequency slip” and associated torque in the rotor shaft 52 corresponds to the level of power delivered to the induction motor 104, 104′ from the synchronous AC generator 56, 56.1, 56.1′, as described hereinabove. Otherwise, from step (1110), if the rotational speed, or corresponding frequency f_(GENERATOR) of the synchronous AC generator 56, 56.1, 56.1′ is not greater than or equal to the corresponding rotational speed, or corresponding frequency f_(MOTOR) of the induction motor 104, 104′, then, in step (1116), the wastegate valve 36 is closed, which causes exhaust gases 28.1 entering the inlet 22 of the turbo-compounder 20 to flow through the turbine nozzle 44 and across the bladed turbine rotor 48, thereby causing rotational acceleration of the bladed turbine rotor 48, so as to provide for the rotational speed, or corresponding frequency f_(GENERATOR) of the synchronous AC generator 56, 56.1, 56.1′ to become greater than or equal to the corresponding rotational speed, or corresponding frequency f_(MOTOR) of the induction motor 104, 104′. Then, the startup process 1100 proceeds with step (1108) and continues therefrom as described hereinabove.

The genset engine 16, 16′ may be shut down without first decoupling the turbo-electric turbo-compounding system 10, 10.2 from the genset engine 16, 16′—i.e. by opening the wastegate valve 36 and deactivating the electrically-controlled clutch 124, —provided that the wastegate valve 36 is opened and the electrically-controlled clutch 124 is deactivated prior to the next startup.

Alternatively, referring to FIGS. 12a and 12b , the turbo-electric turbo-compounding system 10, 10.2 may be disabled without first shutting down the genset engine 16, 16′. Referring to FIG. 12a in accordance with a first embodiment of a shutdown process 1200 for decoupling the second aspect of the turbo-electric turbo-compounding system 10, 10.2, from step (1202), with the genset engine 16, 16′ running, the wastegate valve 36 closed and the electrically-controlled clutch 124 activated, in step (1204), the wastegate valve 36 is opened so as to prevent a subsequent overspeed of the bladed turbine rotor 48 upon removal of the associated electrical load from the synchronous AC generator 56, 56.1, 56.1′. As a result, the exhaust gases 28 are bypassed around the bladed turbine rotor 48, the latter of which then decelerates from a rotational speed for which the associated frequency of the f_(GENERATOR) of the synchronous AC generator 56, 56.1, 56.1′ was in excess of the frequency f_(MOTOR), of the induction motor 104, 104′ by an initial amount of “frequency slip”. In step (1206), the rotational speed, or corresponding output frequency f_(GENERATOR), of the synchronous AC generator 56, 56.1, 56.1′ sensed by the associated first rotational speed or frequency sensor 114 is compared with the corresponding rotational speed, or corresponding frequency f_(MOTOR), of the induction motor 104, 104′, sensed by the associated second rotational speed or frequency sensor 116. If, and when, in step (1208), the rotational speed, or corresponding output frequency f_(GENERATOR) of the synchronous AC generator 56, 56.1, 56.1′ is less than or equal to the corresponding rotational speed, or corresponding frequency f_(MOTOR) of the induction motor 104, 104′—indicative of negligible associated phase current—then, in step (1210), the electrically-controlled clutch 124 is deactivated so as to disconnect the induction motor 104, 104′ from the genset engine 16, 16′, thereby effectively removing the electrical load from the synchronous AC generator 56, 56.1, 56.1′. Otherwise the process repeats with step (1206) until the condition of step (1208) is satisfied.

Alternatively, referring to FIG. 12b , a second embodiment of a shutdown process 1200′ for decoupling the second aspect of the turbo-electric turbo-compounding system 10, 10.2 is the same as the above-described first embodiment of the shutdown process 1200 except that steps (1206) and (1208) of the first embodiment 1200 are respectively replaced with steps (1212) and (1214) of the second embodiment 1200′, the latter which provide for determining when to deactivate the electrically-controlled clutch 124 explicitly responsive to a measurement—from the associated phase current sensor 123, 123′—of phase current I_(PHASE) from the synchronous AC generator 56, 56.1, 56.1′ to the induction motor 104, 104′ for one of the corresponding phases A, B, C. More particularly, following above-described step (1204), in step (1212), the phase current I_(PHASE) from the synchronous AC generator 56, 56.1, 56.1′ to the induction motor 104, 104′ of one of the phases A, B or C is explicitly measured by the phase current sensor 123, 123′ with the electrically-controlled clutch 124 activated. Then, in step (1214), if the phase current I_(PHASE) is less than a threshold, then, in step (1210), the electrically-controlled clutch 124 deactivated. Otherwise, the process repeats with step (1212) until the condition of step (1214) is satisfied. Accordingly, the second embodiment of the shutdown process 1200′ explicitly provides for deactivating the electrically-controlled clutch 124 at a zero or near-zero current condition.

Referring to FIG. 13, in accordance with a third aspect of the turbo-electric turbo-compounding system 10, 10.3, the synchronous AC generator 56, 56.1, 56.1′ is connected to the induction motor 104, 104′ via an associated solid-state switching system 125—or, more generally, a solid-state control system, —the latter of which is under control of a controller 112, and optionally also via an associated contactor 110, 110′—also under control of the controller 112—either between the synchronous AC generator 56, 56.1, 56.1′ and the solid-state switching system 125, or between the solid-state switching system 125 and the induction motor 104, 104′. The third aspect of the turbo-electric turbo-compounding system 10, 10.3 operates the same as described hereinabove for the first aspect of the turbo-electric turbo-compounding system 10, 10.3 in respect of the elements common therebetween. The solid-state switching system 125 provides for actively limiting the current in each phase A, B, C (i.e. the associated phase current) responsive to measurements of either frequency, output voltage or output power of the synchronous AC generator 56, 56.1, 56.1′, frequency of the induction motor 104, 104′ or phase current in accordance with known control system design practice so as to provide for achieving stability more quickly than otherwise possible without the solid-state switching system 125. For example, the magnitude of the phase current would affect the overall open-loop gain of an associated speed-control system, which would there affect the stability of the associated speed-control system. The solid-state switching system 125 provides for additional torque control responsive to power or phase-current switching, so as to control the effective level of current from the synchronous AC generator 56, 56.1, 56.1′ to the induction motor 104, 104′, so as to either improve stability, or provide for controlling the ratio of rotational speed of the synchronous AC generator 56, 56.1, 56.1′ to the rotational speed of the induction motor 104, 104′ in order to provide for improved operating efficiency. The contactor 110, 110′ would be optional if the solid-state switching system 125 were configured to provide for switching the associated phase current completely off. As with the first 10.1 and second 10.2 aspects, in accordance with the third aspect 10.3, the maximum level of phase current is also limited by the amount of “frequency slip” between the synchronous AC generator 56, 56.1, 56.1′ and the induction motor 104, 104′.

Referring to FIGS. 14 and 15, in accordance with a fourth aspect of a turbo-electric turbo-compounding system 10, 10.4, the synchronous AC generator 56, 56.1, 56.1′ is replaced with an asynchronous AC generator 126, for example, an induction generator 126′, for example, a three-phase induction generator 126″, —or more generally, a multi-phase induction generator comprising at least three phases, wherein the number of phases is the same as the corresponding above-described multi-phase induction motor—that is directly connected to the induction motor 104, 104′, wherein excitation to the induction generator 126′, 126″ is provided by an associated induction generator inverter 128 under control of a controller 112. To the extent that the induction generator inverter 128 would not provide for preventing the generation of power by the asynchronous AC generator 126, 126′, 126″, the latter may optionally be interconnected to the induction generator 126′, 126″ via an associated contactor 110, 110′, under control of the controller 112 in the same manner as described hereinabove for the first aspect of the turbo-electric turbo-compounding system 10, 10.1.

An induction generator 126′, 126″ is similar in construction to an induction motor, but, in order to generate power, is rotated above the synchronous speed associated with an AC excitation 130 that is simultaneously applied to the phases A, B, C thereof, and which is otherwise unable to generate power absent the applied AC excitation 130. The AC excitation 130 is generated by the induction generator inverter 128 that generates controllable-frequency three-phase power from electrical power provided by a DC Power Supply 132, for example, a battery 132′, at a frequency that is less than the synchronous frequency corresponding to the rotational speed of the synchronous AC generator 56.

For example, referring to FIGS. 16 and 17, in accordance with one set of embodiments, the induction generator inverter 128 incorporates an excitation frequency control system 134 that provides for controlling the frequency of the AC excitation 130 applied to the phases A, B, C of the asynchronous AC generator 126, 126′, 126″. More particularly, a frequency command signal 136 is generated by subtracting 138 a frequency-slip command signal 140 from a synchronous frequency signal 142 that is determined by a speed-to-frequency transformation 144 of a rotational speed signal 146 from the rotational-speed sensor 114 of the asynchronous AC generator 126, 126′, 126″. In one set of embodiments, the frequency-slip command signal 140 is a function of the rotational speed of the asynchronous AC generator 126, 126′, 126″, e.g. as given by the first rotational-speed or frequency signal 118, and is adapted so as to provide for frequency-slip to increase with increasing rotational speed. The frequency of the three-phase output signal 148 of an associated three-phase inverter 150 is then set to the frequency of the corresponding frequency-slip command signal 140, or more generally, a multi-phase output signal of an associated multi-phase inverter, comprising at least three phases, wherein the number of phases is the same as the number of phases of the associated multi-phase asynchronous AC generator 126.

The torque generated by the induction motor 104, 104′ is responsive to the associated frequency slip thereof, i.e. the amount by which the frequency of the AC power generated by the asynchronous AC generator 126, 126′, 126″ exceeds the synchronous frequency corresponding to the rotational speed of the induction motor 104, 104′, wherein the frequency of the AC power generated by the asynchronous AC generator 126, 126′, 126″ is responsive to the rotational speed thereof. The amount of current generated by the asynchronous AC generator 126, 126′, 126″—and the associated resulting torque generated by the induction motor 104, 104′—is responsive to the frequency slip thereof, i.e. the amount by which the synchronous frequency corresponding to the rotational speed of the asynchronous AC generator 126, 126′, 126″ exceeds the frequency of the three-phase output signal 148 from the three-phase inverter 150.

For example, FIG. 18 illustrates a graph of shaft torque 152 as a function of rotational speed 154 relative to the associated synchronous rotational speed 154 ^(s) for a generic induction motor—representative of the induction motor 104, 104′, —in a motoring mode 156.1 of operation, wherein shaft torque 152 produced by the induction motor 104, 104′ increases with increasing frequency slip 158 up to a maximum possible shaft torque 152.1, referred to as a “breakover torque”, which occurs at an associated rotational speed 154.1 and frequency slip 158.1. The shaft torque 152 decreases with further increasing frequency slip 158, wherein the minimum shaft torque 152.2 occurs at stall, i.e. zero rotational speed 154.2. Accordingly, the induction motor 104, 104′ is designed so that at any operating rotational speed 154, the maximum shaft torque 152 during operation thereof is less than the corresponding associated breakover shaft torque 152.1.

Furthermore, FIG. 19 illustrates a graph of shaft torque 152 as a function of rotational speed 154 relative to the associated synchronous rotational speed 154 ^(s), for a generic induction machine in all modes of operation, including the motoring mode 156.1 illustrated in FIG. 18 representative of the induction motor 104, 104′, a generating mode 156.2 representative of the induction generator 126′, 126″, and, for completeness, a braking mode 156.3. The various modes of operation are delineated with respect to the value of a normalized slip parameter s, defined as follows:

$\begin{matrix} {{s = \frac{\left( {n_{s} - n} \right)}{n_{s}}},} & (1) \end{matrix}$ wherein n_(s) is the synchronous rotational speed 154 ^(s), n is the rotational speed 154, and frequency slip 158 is proportional to (n_(s)−n). Accordingly, for s>1, the induction machine operates in the braking mode 156.3; for 0<s<1, the induction machine operates in the motoring mode 156.1; and for s<0, the induction machine operates in the generating mode 156.2. For the induction generator 126′, 126″—which operates in the generating mode 156.2—the rotational speed 154 is greater than the synchronous rotational speed 154 ^(s), and the magnitude of the shaft torque 152 increases with increasing magnitude of frequency slip 158 up to a maximum possible shaft torque 152.1′, also referred to as a “breakover torque”, which occurs at an associated rotational speed 154.1′ and frequency slip 158.1′, and decreases with further increasing magnitude of frequency slip 158.

For the induction generator 126′, the synchronous frequency is provided by the induction generator inverter 128. The induction generator 126′ operates at a rotational speed 154 above the corresponding synchronous rotational speed 154 ^(s), and the induction motor 104, 104′ operates at a rotational speed 154 below the corresponding synchronous rotational speed 154 ^(s), in order to provide for torque to be effectively transmitted from the induction generator 126 to the induction motor 104, 104′. Furthermore, in one set of embodiments, the voltage from the induction generator inverter 128 excitation source is adjusted so that the output of the induction generator 126′ operates with a nearly constant ratio of frequency to voltage, in the same manner as described hereinabove for the permanent magnet AC generator 56.1′. Accordingly, the induction generator inverter 128 provides both for an appropriate amount of frequency slip, and for controlling the output voltage of the induction generator 126′ as a function of frequency. One example of a control system that provides for this functionality in the contexts of a hybrid vehicle is disclosed in Application Note No. AN1930 entitled “3-Phase AC Induction Motor Vector Control Using a 56F80x, 56F8100 or 56F8300 Device” by Jaroslav Lepda and Petr Stekl, published by Freescale Semiconductor, Rev. Feb. 2, 2005, which is incorporated by reference herein in its entirety.

For comparison, the rotational speed 154 of the bladed turbine rotor 48 would be higher when used with an induction generator 126′ than when used with a permanent magnet AC generator 56.1′ at any corresponding loaded operating point of the induction motor 104, 104′.

For an asynchronous AC generator 126, 126′, 126″ comprising an induction generator 126′, 126″, the associated frequency-slip command signal 140 is automatically controlled by the controller 112 to a level responsive to the rotational speed thereof, for example, directly related, e.g. proportional to the rotational speed of the bladed turbine rotor 48/asynchronous AC generator 126, 126′, 126″, so that the amount of frequency slip increases with increasing rotational speed. The generated AC electrical power from the induction generator 126′, 126″ drives the induction motor 104, 104′ at a rotational speed that is inherently determined by the induction motor 104, 104′ responsive to the torque on the shaft of the rotor 106 of the induction motor 104, 104′ that supplies power to the genset engine 16, 16′ via the gearbox 108 therebetween. For a given frequency of the applied AC electrical power from the asynchronous AC generator 126, 126′, 126″—which is determined by the rotational speed thereof, —the amount of frequency slip of the induction motor 104, 104′ increases with torque, resulting in a corresponding increase in current to the induction motor 104, 104′, which inherently acts to provide for the induction motor 104, 104′ to operate at a corresponding stable rotational speed corresponding to the given level of torque. Accordingly, for any given state of operation of the genset engine 16, 16′, the induction motor 104, 104′ will inherently seek a corresponding rotational speed that depends upon the corresponding level of torque provided thereby to the genset engine 16, 16′.

Referring further to FIG. 17, in one set of embodiments, the induction generator inverter 128 generates the three-phase output signal 148 by boosting the voltage of the DC-power input 160 from the DC Power Supply 132 with an inverter/voltage boost circuit 162, so as to generate a relatively-high voltage supply on a high-voltage bus 164 that is provided through a current control circuit 166 to power a set of three-phase bridge power transistors 168, or more generally, a set of multi-phase bridge power transistors, comprising at least three phases, wherein the number of phases is the same as the number of phases of the associated multi-phase asynchronous AC generator 126. For example, the voltage boost of the inverter/voltage boost circuit 162 can be provided for by either magnification of an AC signal using a transformer, or by any of various known pulse-based voltage magnification techniques, for example, as used by known voltage doubler or charge pump circuits, wherein the resulting level of the voltage of the high-voltage bus 164 can be either fixed, i.e. DC, or fluctuating. The waveform of a sinusoidal signal at the frequency of the frequency command signal 136 is then synthesized and phase shifted 170 so as to generate the three phases at a frequency that provides for the necessary torque from the induction motor 104, 104′, and then input to a three-phase driver 172—or more generally, a multi-phase driver, comprising at least three phases, wherein the number of phases is the same as the number of phases of the associated multi-phase asynchronous AC generator 126—that provides for driving the three-phase bridge power transistors 168, for example, by pulse-modulation or pulse width modulation, so that the switched output of the three-phase bridge power transistors 168—powered from the high-voltage bus 164—provides the corresponding three-phase output signal 148, possibly including filtering by an associated filtering network in conjunction with the inductance of the windings of the asynchronous AC generator 126, 126′, 126″ and induction motor 104, 104′.

The induction motor 104, 104′ operates at a rotational speed for which the corresponding associated synchronous frequency is less than the frequency of the output frequency of the asynchronous AC generator 126, 126′, 126″, wherein the magnitude of the frequency slip increases with load as necessary to generate the required torque in the shaft of the rotor 106 of the induction motor 104, 104′, the same as for the first aspect. Under no-load conditions, frequency slip will be nearly zero, but non-zero as a result of parasitic losses, friction, and windage in the induction motor 104, 104′; and the ratio of the rotational speeds of the induction motor 104, 104′ and the asynchronous AC generator 126, 126′, 126″ is determined by the ratio of the number of poles of the respective electrical machines.

It should be understood that that the solid-state switching system 125 of the third aspect of the turbo-electric turbo-compounding system 10, 10.3—an extension to the first aspect of the turbo-electric turbo-compounding system 10, 10.1—may also be used in cooperation with the second 10.2 or fourth 10.4 aspects of the turbo-electric turbo-compounding system 10, so as to provide either for enhanced speed control or for improved efficiency. Generally, the activation of the turbo-electric turbo-compounding system 10, 10.1, 10.2, 10.3, 10.4 in accordance with any of the first 10.1 through fourth 10.4 aspects is controlled by initially decoupling the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator from the genset engine 16, 16′—either electrically or mechanically, depending upon the aspect—and opening the wastegate valve 36, prior to starting the genset engine 16, 16′. Then, after starting the genset engine 16, 16′, the rotational speeds of the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator and the induction motor 104, 104′ are compared, and the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator and the genset engine 16, 16′ are coupled when the frequency of the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator meets or exceeds the frequency of the induction motor 104, 104′—thereby satisfying an associated coupling-speed condition, —wherein if the frequency of the latter initially exceeds that of the former, the wastegate valve 36 is closed so that the coupling-speed condition can be met. If not already closed, the wastegate valve 36 is closed after the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator is coupled to the genset engine 16, 16′.

More particularly, referring to FIG. 20, in accordance with a generic startup process 2000 for controlling the startup of a genset 12 in cooperation with any of the first 10.1 through fourth 10.4 aspects of the turbo-electric turbo-compounding system 10, in step (2002), the wastegate valve 36 is initially open so as to provide for the exhaust gases 28 to flow relatively unimpeded through the turbo-compounder 20 without acting upon the bladed turbine rotor 48. In step (2004), the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator is decoupled from the genset engine 16, 16′, for example, either a) by opening the contactor 110, 110′ associated with the first aspect 10.1, and optionally associated with the third 10.3 or fourth 10.4 aspects, b) by deactivating the electrically-controlled clutch 124 associated with the second aspect 10.2, c) by nulling the phase current with the solid-state switching system 125 of the third aspect 10.3, or d) by nulling the associated AC excitation 130 from the induction generator inverter 128 of the fourth aspect 10.4; so as to prevent an electrical loading of the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator by the induction motor 104, 104′, or a mechanical loading of the induction motor 104, 104′ by the genset engine 16, 16′, which thereby prevents a more than insubstantial amount of electrical power from being extracted from the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator. As a result, the exhaust gases 28, 28.1, 28.2 can flow through the turbine nozzle 44 and across the bladed turbine rotor 48 without substantial loss. Accordingly, following step (2004), the exhaust gases 28 flowing through the turbo-electric turbo-compounding system 10, 10.2 will either bypass the bladed turbine rotor 48 or flow thereacross without causing a substantial electrical load on the synchronous AC generator 56, 56.1, 56.1′, so as to provide for minimum back pressure in the exhaust discharge conduit 26, and thereby not impede a startup of the genset engine 16, 16′, if the genset engine 16, 16′ is not already running. Then, in step (2006), if not already started, the genset engine 16, 16′ is started; and, if not already running at rated speed, the genset engine 16, 16′ is run at rated speed, so as to provide for the generation of electrical power by the genset main generator 18.

Then, in step (2008), the first rotational-speed or frequency signal 118 of the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator, sensed by the associated first rotational speed or frequency sensor 114, is compared with the corresponding second rotational-speed or frequency signal 120 associated with the induction motor 104, 104′. If, in step (2010), the rotational speed, or corresponding frequency f_(GENERATOR) of the synchronous AC generator 56, 56.1, 56.1′ is greater than or equal to the corresponding rotational speed, or corresponding frequency f_(MOTOR) of the induction motor 104, 104′—indicative of a prospective positive “frequency slip” condition—then, in step (2012), the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator is coupled to the genset engine 16, 16′, for example, either a) by closing the contactor 110, 110′ associated with the first aspect 10.1, and optionally associated with the third 10.3 or fourth 10.4 aspects, b) by activating the electrically-controlled clutch 124 associated with the second aspect 10.2, c) by providing for non-zero phase current by action of the solid-state switching system 125 of the third aspect 10.3, or d) by providing an associated AC excitation 130 from the induction generator inverter 128 of the fourth aspect 10.4; so as to provide for the genset engine 16, 16′ to load the induction motor 104, 104′, and for the induction motor 104, 104′ to load the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator, which in turn, loads the bladed turbine rotor 48, initially causing a rotational deceleration thereof if rotating. Alternatively, the coupling of the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator to the genset engine 16, 16′ may also be dependent upon the absolute rotational speed of the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator exceeding a threshold level, for example, given as a particular percentage of rated rotational speed. Then, in step (2014), the wastegate valve 36 is closed fully, which causes substantially all of the exhaust gases 28.1 entering the inlet 22 of the turbo-compounder 20 to flow through the turbine nozzle 44 and across the bladed turbine rotor 48, thereby causing rotational acceleration of the bladed turbine rotor 48, so as to provide for the latter to reach an equilibrium speed for which the “frequency slip” and associated torque in the rotor shaft 52 corresponds to the level of power delivered to the induction motor 104, 104′ from the synchronous AC generator 56, 56.1, 56.1′, as described hereinabove. Otherwise, from step (2010), if the rotational speed, or corresponding frequency f_(GENERATOR) of the synchronous AC generator 56, 56.1, 56.1′ is initially not greater than or equal to the corresponding rotational speed, or corresponding frequency f_(MOTOR) of the induction motor 104, 104′, then, in step (2016), the wastegate valve 36 is closed, which causes exhaust gases 28.1 entering the inlet 22 of the turbo-compounder 20 to flow through the turbine nozzle 44 and across the bladed turbine rotor 48, thereby causing rotational acceleration of the bladed turbine rotor 48, so as to provide for the rotational speed, or corresponding frequency f_(GENERATOR) of the synchronous AC generator 56, 56.1, 56.1′ to become greater than or equal to the corresponding rotational speed, or corresponding frequency f_(MOTOR) of the induction motor 104, 104′. Then, the startup process 2000 proceeds with step (2008) and continues as described hereinabove. Following step (2014), in step (2018), for the third aspect 10.3, the phase current is controlled by the solid-state switching system 125 so as to provide for either stable speed control or improved efficiency, and for the fourth aspect 10.4, the frequency slip of the AC excitation 130 is controlled by the excitation frequency control system 134 so as to provide for the associated asynchronous AC generator 126, 126′, 126″ to generate power.

The genset engine 16, 16′ may be shut down without first decoupling the turbo-electric turbo-compounding system 10, 10.2 provided that the wastegate valve 36 is opened and the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator is decoupled from the genset engine 16, 16′ prior to the next startup.

Alternatively, referring to FIGS. 21a and 21b , the turbo-electric turbo-compounding system 10, 10.1, 10.2, 10.3, 10.4 may be disabled without shutting down the genset engine 16, 16′. Referring to FIG. 21a in accordance with a first embodiment of a generic shutdown process 2100 for decoupling the first 10.1 through fourth 10.4 aspects of the turbo-electric turbo-compounding system 10, from step (2102) with the genset engine 16, 16′ running, the wastegate valve 36 closed and the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator coupled to the genset engine 16, 16′, in step (2104), the wastegate valve 36 is opened so as to prevent a subsequent overspeed of the bladed turbine rotor 48 upon removal of the associated electrical load from the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator or mechanical load from the induction motor 104, 104′. As a result, the exhaust gases 28 are bypassed around the bladed turbine rotor 48, the latter of which then decelerates from a rotational speed for which the associated frequency of the f_(GENERATOR) of the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator was in excess of the frequency f_(MOTOR) of the induction motor 104, 104′ by a given amount of “frequency slip”. In step (2106), the rotational speed, or corresponding output frequency f_(GENERATOR), of the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator sensed by the associated first rotational speed or frequency sensor 114 is compared with the rotational speed, or corresponding frequency f_(MOTOR), of the induction motor 104, 104′ sensed by the associated second rotational speed or frequency sensor 116. If, and when, in step (2108), the rotational speed, or corresponding output frequency f_(GENERATOR) of the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator is less than or equal to the corresponding rotational speed, or corresponding frequency f_(MOTOR) of the induction motor 104, 104′—indicative of negligible associated phase current—then, in step (2110), the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator is decoupled from the genset engine 16, 16′, thereby effectively removing the electrical load from the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator. Otherwise, the process repeats with step (2106) until the condition of step (2108) is satisfied.

Alternatively, referring to FIG. 21b , a second embodiment of a generic shutdown process 2100′ for decoupling the first 10.1 through fourth 10.4 aspects of the turbo-electric turbo-compounding system 10 is the same as the above-described first embodiment of the generic shutdown process 2100 except that steps (2106) and (2108) of the first embodiment 2100 are respectively replaced with steps (2112) and (2114) of the second embodiment 2100′, the latter which provide for determining when to decouple the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator from the genset engine 16, 16′ explicitly responsive to a measurement—from the associated phase current sensor 123, 123′—of phase current I_(PHASE) from the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator to the induction motor 104, 104′ for one of the corresponding phases A, B, C. More particularly, following above-described step (2104), in step (2112) the phase current I_(PHASE) from the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator to the induction motor 104, 104′ of one of the phases A, B or C is explicitly measured by the phase current sensor 123, 123′ with the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator coupled to the induction motor 104, 104′. Then, in step (2114), if the phase current I_(PHASE) is less than a threshold, then, in step (2110), the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator is decoupled from the induction motor 104, 104′. Otherwise, the process repeats with step (2112) until the condition of step (2114) is satisfied. Accordingly, the second embodiment of the shutdown process 2100′ explicitly provides for decoupling the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator from the induction motor 104, 104′ at a zero or near-zero current condition.

It should be understood that determination of when to couple or decouple the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator and the genset engine 16, 16′—i.e. as provided for by steps (810-812), (906-908), (1108-1110), (1206-1208), (2008-2010) or (2106-2108)—could be either responsive to frequency as indicated, or responsive to speed, taking into account the difference in speeds of the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator and induction motor 104, 104′ which depends upon the associated pole ratio thereof, and taking into account the effective pole counts of the corresponding first 114 and second 116 rotational speed or frequency sensors.

Alternatively, for purposes of decoupling the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator and the genset engine 16, 16′, this determination can be responsive to phase current directly, wherein the decoupling transition is made when a measured phase current is less than a threshold, for example, at or near zero. The use of phase current to control the decoupling of the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator and the genset engine 16, 16′ is expected to improve stability of the associated control system, which might otherwise be subject to oscillations if the decoupling is controlled responsive to measurements of frequency or rotational speed. Furthermore, it should be understood that as either an alternative, or an addition, to the above-described bang-bang control of the wastegate valve 36, the wastegate valve 36 may also be controlled—for example, either continuously or by pulse modulation—so as to provide for modulating the power output of the associated synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator, for example, so as to provide for the stability thereof, in which case, the associated phase-current sensor 123, 123′ can be used in cooperation therewith to provide a measure of the load on the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator as a result of the electrical power supplied thereby to the genset engine 16, 16′ via the induction motor 104.

The above-described shutdown processes 900, 900′, 1200, 1200′, 2100, 2100′ presume that the wastegate valve 36 has sufficient flow area to provide for bypassing the exhaust gases 28, 28.1 with sufficiently low resulting associated pressure drop across the bladed turbine rotor 48 so that the bladed turbine rotor 48 does not undergo an over-speed condition when the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator is decoupled from the genset engine 16, 16′. Alternatively, prior to opening the wastegate valve 36 in steps (904), (1204) or (2104), it may be beneficial to first reduce the speed or power level of the genset engine 16, 16′ until a speed or power level is reached for which the bladed turbine rotor 48 will not undergo an over-speed condition when the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator is decoupled from the genset engine 16, 16′ with the wastegate valve 36 open.

It should be understood that the means for coupling power from the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator to the genset engine 16, 16′—e.g. the contactor 110, 110′, electrically-controlled clutch 124, or the solid-state switching system 125—need not necessarily be disconnected when either commencing or terminating the operation of recovering power from the flow of exhaust gases 28, but instead, it is anticipated that the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator will naturally synchronize with the induction motor 104, 104′ during the associated transient operation.

The turbo-electric turbo-compounding system 10 may further incorporate a provision for detecting if the electrical load on the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator becomes disconnected—for example, as a result of failure of either the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator, the induction motor 104, 104′, an interconnecting element therebetween, or a mechanical coupling between the induction motor 104, 104′ and the genset engine 16, 16′—and opening the wastegate valve 36 if the electrical load becomes disconnected so as to prevent an overspeed of the bladed turbine rotor 48.

It should be understood that the exhaust gases 28 could alternatively be first collected in a volute/scroll or other collector, and discharged from the turbo-compounder 20 away from the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator, without first flowing through the annular plenum 74 surrounding the core housing structure 60, so as to provide for reducing the associated heat load to the synchronous 56, 56.1, 56.1′ or asynchronous 126, 126′, 126″ AC generator.

Notwithstanding that the turbo-electric turbo-compounding system 10, 10.1, 10.2, 10.3, 10.4 has been described in cooperation with a genset engine 16, 16′ driving a genset main generator 18, it should be understood that the turbo-electric turbo-compounding system 10, 10.1, 10.2, 10.3, 10.4 is not limited to genset applications, and further, could be used with any type of heat engine that exhausts a flow of gas through a fluid conduit from which energy might be extracted so as to provide for improving the thermal efficiency thereof, including, but not limited to reciprocating engines operating under either a Diesel, Otto or Atkinison cycle, or a gas-turbine engine operating under a Brayton cycle. The turbo-electric turbo-compounding system 10, 10.1, 10.2, 10.3, 10.4 is well suited for application in engines that experience relatively long periods at relatively steady speeds, such as, but not limited to, gensets, marine engines (e.g. large marine engines used in cargo ships), and truck engines (e.g. long-haul on-highway truck engines).

It should be understood that for each above-described embodiment illustrated with a three-phase device or signal, that, in general, a corresponding multi-phase device or signal could also be used, wherein, the number of phases is at least three and is the same for all associated devices and signals, so as to provide for determinacy in respect of the directions of rotation of the generator and the induction motor, i.e. so as to guarantee that the associated induction motor will always rotate in the same direction responsive to a signal from the associated generator.

While specific embodiments have been described in detail in the foregoing detailed description and illustrated in the accompanying drawings, those with ordinary skill in the art will appreciate that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. It should be understood, that any reference herein to the term “or” is intended to mean an “inclusive or” or what is also known as a “logical OR”, wherein when used as a logic statement, the expression “A or B” is true if either A or B is true, or if both A and B are true, and when used as a list of elements, the expression “A, B or C” is intended to include all combinations of the elements recited in the expression, for example, any of the elements selected from the group consisting of A, B, C, (A, B), (A, C), (B, C), and (A, B, C); and so on if additional elements are listed. Furthermore, it should also be understood that the indefinite articles “a” or “an”, and the corresponding associated definite articles “the” or “said”, are each intended to mean one or more unless otherwise stated, implied, or physically impossible. Yet further, it should be understood that the expressions “at least one of A and B, etc.”, “at least one of A or B, etc.”, “selected from A and B, etc.” and “selected from A or B, etc.” are each intended to mean either any recited element individually or any combination of two or more elements, for example, any of the elements from the group consisting of “A”, “B”, and “A AND B together”, etc. Yet further, it should be understood that the expressions “one of A and B, etc.” and “one of A or B, etc.” are each intended to mean any of the recited elements individually alone, for example, either A alone or B alone, etc., but not A AND B together. Furthermore, it should also be understood that unless indicated otherwise or unless physically impossible, that the above-described embodiments and aspects can be used in combination with one another and are not mutually exclusive. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims, and any and all equivalents thereof. 

What is claimed is:
 1. A method of recovering power from a flow of exhaust from an internal combustion engine, comprising: a. receiving the flow of exhaust from the internal combustion engine; b. controlling a division of said flow of exhaust from said internal combustion engine between first and remaining second portions of said flow of exhaust, wherein each of said first and remaining second portions of said flow of exhaust is greater than or equal to none of said flow of exhaust, and less than or equal to all of said flow of exhaust; c. causing said first portion of said flow of exhaust, if greater than zero, to impinge upon a plurality of blades of a bladed turbine rotor; d. causing said remaining second portion of said flow of exhaust, if greater than zero, to bypass said plurality of blades of said bladed turbine rotor; e. driving a generator with said bladed turbine rotor responsive said first portion of said flow of exhaust, if greater than zero, impinging upon said plurality of blades of said bladed turbine rotor; f. operatively coupling an electrical output of said generator to an induction motor so as to provide for powering said induction motor with electrical power generated by said generator; and g. operatively mechanically coupling an output shaft of said induction motor to an output shaft of said internal combustion engine so as to provide for recovering power from said first portion of said flow of exhaust, wherein when commencing the operation of recovering said power from said first portion of said flow of exhaust, said division of said flow of exhaust is controlled so that said remaining second portion of said flow of exhaust includes all of said flow of exhaust received from said internal combustion engine that will flow through said associated open wastegate valve at said associated operating condition of said internal combustion engine.
 2. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 1, wherein said generator comprises a multi-phase A.C. synchronous generator, said induction motor comprises a multi-phase induction motor, the number of phases of said multi-phase induction motor is at least three and equal in number to the number of phases of said multi-phase A.C. synchronous generator, each phase of said multi-phase induction motor is electrically associated with a corresponding phase of said multi-phase A.C. synchronous generator.
 3. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 2, wherein at least one of the operations selected from the group consisting of the operation of operatively coupling said electrical output of said generator to said induction motor and the operation of operatively mechanically coupling said output shaft of said induction motor to said output shaft of said internal combustion engine provides for decoupling said generator from said internal combustion engine when either commencing or terminating the operation of recovering said power from said first portion of said flow of exhaust, and provides for operatively coupling said generator to said internal combustion engine when recovering said power from said first portion of said flow of exhaust.
 4. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 3, wherein the operation of commencing the operation of recovering said power from said first portion of said flow of exhaust comprises: a. controlling said division of said flow of exhaust so that said remaining second portion of said flow of exhaust includes all of said flow of exhaust received from said internal combustion engine that will flow through said associated open wastegate valve at said associated operating condition of said internal combustion engine; b. decoupling said generator from said internal combustion engine; c. if not already started, starting said internal combustion engine and running said internal combustion engine at a rated speed; d. comparing a first signal responsive to a frequency or rotational speed of said generator, with a corresponding second signal responsive to a corresponding frequency or rotational speed of said induction motor; and e. if said first signal is greater than or equal to said second signal, then operatively coupling said generator to said internal combustion engine so as to provide for said generator to supply said power to said internal combustion engine; f. otherwise, or if not already provided for, controlling said division of said flow of exhaust so that said first portion of said flow of exhaust includes at least a substantial portion of said flow of exhaust received from said internal combustion engine.
 5. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 3, wherein the operation of terminating the operation of recovering said power from said first portion of said flow of exhaust comprises: a. controlling said division of said flow of exhaust so that said remaining second portion of said flow of exhaust includes all of said flow of exhaust received from said internal combustion engine that will flow through said associated open wastegate valve at said associated operating condition of said internal combustion engine; b. comparing a first signal responsive to a frequency or rotational speed of said generator, with a corresponding second signal responsive to a corresponding frequency or rotational speed of said induction motor; and c. if said first signal is less than or equal to said second signal, then decoupling said generator from said internal combustion engine so as to prevent said generator from supplying said power to said internal combustion engine.
 6. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 3, wherein the operation of terminating the operation of recovering said power from said first portion of said flow of exhaust comprises: a. controlling said division of said flow of exhaust so that said remaining second portion of said flow of exhaust includes all of said flow of exhaust received from said internal combustion engine that will flow through said associated open wastegate valve at said associated operating condition of said internal combustion engine; b. comparing a measure of phase current with a threshold, wherein said measure of phase current is responsive to a measurement of phase current in a conductor that electrically connects a phase of said generator to a corresponding phase of said induction motor; and c. if said measure of phase current is less than said threshold, then decoupling said generator from said internal combustion engine so as to prevent said generator from supplying said power to said internal combustion engine.
 7. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 2, wherein the operation of operatively coupling said electrical output of said generator to said induction motor comprises operatively coupling said electrical output of said generator to said induction motor through at least one contactor, relay or solid-state switching or control system that provides for decoupling said generator from said internal combustion engine, and that provides for operatively coupling said generator to said internal combustion engine, responsive to a control signal.
 8. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 2, wherein the operation of operatively mechanically coupling said output shaft of said induction motor to said output shaft of said internal combustion engine comprises mechanically coupling said output shaft of said induction motor to said output shaft of said internal combustion engine through an electrically-controlled clutch that provides for decoupling said generator from said internal combustion engine, and that provides for operatively coupling said generator to said internal combustion engine, responsive to a control signal.
 9. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 2, further comprising controlling said division of said flow of exhaust so that said remaining second portion of said flow of exhaust includes all of said flow of exhaust received from said internal combustion engine that will flow through said associated open wastegate valve at said associated operating condition of said internal combustion engine, if said electrical output of said generator becomes disconnected during the operation of recovering said power from said flow of exhaust.
 10. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 2, further comprising operating said multi-phase induction motor at a rotational speed that is lower than a rotational speed of said multi-phase A.C. synchronous generator by an amount greater than might otherwise result from frequency slip, responsive to a difference in a number of poles therebetween.
 11. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 1, wherein said generator comprises a multi-phase induction generator, said induction motor comprises a multi-phase induction motor, the number of phases of said multi-phase induction motor is at least three and equal in number to the number of phases of said multi-phase induction generator, each phase of said multi-phase induction motor is electrically associated with a corresponding phase of said multi-phase induction generator, further comprising generating a multi-phase excitation signal, wherein a frequency of said multi-phase excitation signal is responsive to a rotational speed of said multi-phase induction generator, and each phase of said multi-phase excitation signal is electrically associated with a corresponding phase of said multi-phase induction generator.
 12. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 11, further comprising operating said multi-phase induction motor at a rotational speed that is lower than a rotational speed of said multi-phase induction generator by an amount greater than might otherwise result from frequency slip, responsive to a difference in a number of poles therebetween.
 13. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 1, wherein at least one of the operations selected from the group consisting of the operation of operatively coupling said electrical output of said generator to said induction motor and the operation of operatively mechanically coupling said output shaft of said induction motor to said output shaft of said internal combustion engine provides for decoupling said generator from said internal combustion engine when either commencing or terminating the operation of recovering said power from said first portion of said flow of exhaust, and provides for operatively coupling said generator to said internal combustion engine when recovering said power from said first portion of said flow of exhaust.
 14. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 13, wherein the operation of commencing the operation of recovering said power from said first portion of said flow of exhaust comprises: a. controlling said division of said flow of exhaust so that said remaining second portion of said flow of exhaust includes all of said flow of exhaust received from said internal combustion engine that will flow through said associated open wastegate valve at said associated operating condition of said internal combustion engine; b. decoupling said generator from said internal combustion engine; c. if not already started, starting said internal combustion engine and running said internal combustion engine at a rated speed; d. comparing a first signal responsive to a frequency or rotational speed of said generator, with a corresponding second signal responsive to a corresponding frequency or rotational speed of said induction motor; and e. if said first signal is greater than or equal to said second signal, then operatively coupling said generator to said internal combustion engine so as to provide for said generator to supply said power to said internal combustion engine; f. otherwise, or if not already provided for, controlling said division of said flow of exhaust so that said first portion of said flow of exhaust includes at least a substantial portion of said flow of exhaust received from said internal combustion engine.
 15. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 13, wherein the operation of terminating the operation of recovering said power from said first portion of said flow of exhaust comprises: a. controlling said division of said flow of exhaust so that said remaining second portion of said flow of exhaust includes all of said flow of exhaust received from said internal combustion engine that will flow through said associated open wastegate valve at said associated operating condition of said internal combustion engine; b. comparing a first signal responsive to a frequency or rotational speed of said generator, with a corresponding second signal responsive to a corresponding frequency or rotational speed of said induction motor; and c. if said first signal is less than or equal to said second signal, then decoupling said generator from said internal combustion engine so as to prevent said generator from supplying said power to said internal combustion engine.
 16. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 13, wherein the operation of terminating the operation of recovering said power from said first portion of said flow of exhaust comprises: a. controlling said division of said flow of exhaust so that said remaining second portion of said flow of exhaust includes all of said flow of exhaust received from said internal combustion engine that will flow through said associated open wastegate valve at said associated operating condition of said internal combustion engine; b. comparing a measure of phase current with a threshold, wherein said measure of phase current is responsive to a measurement of phase current in a conductor that electrically connects a phase of said generator to a corresponding phase of said induction motor; and c. if said measure of phase current is less than said threshold, then decoupling said generator from said internal combustion engine so as to prevent said generator from supplying said power to said internal combustion engine.
 17. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 1, wherein the operation of operatively coupling said electrical output of said generator to said induction motor comprises operatively coupling said electrical output of said generator to said induction motor through at least one contactor, relay or solid-state switching or control system that provides for decoupling said generator from said internal combustion engine, and that provides for operatively coupling said generator to said internal combustion engine, responsive to a control signal.
 18. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 1, wherein the operation of operatively mechanically coupling said output shaft of said induction motor to said output shaft of said internal combustion engine comprises mechanically coupling said output shaft of said induction motor to said output shaft of said internal combustion engine through an electrically-controlled clutch that provides for decoupling said generator from said internal combustion engine, and that provides for operatively coupling said generator to said internal combustion engine, responsive to a control signal.
 19. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 1, further comprising controlling said division of said flow of exhaust so that said remaining second portion of said flow of exhaust includes all of said flow of exhaust received from said internal combustion engine that will flow through said associated open wastegate valve at said associated operating condition of said internal combustion engine, if said electrical output of said generator becomes disconnected during the operation of recovering said power from said flow of exhaust.
 20. A method of recovering power from a flow of exhaust from an internal combustion engine as recited in claim 1, wherein when terminating the operation of recovering said power from said first portion of said flow of exhaust, said division of said flow of exhaust is controlled so that said remaining second portion of said flow of exhaust includes all of said flow of exhaust received from said internal combustion engine that will flow through an associated open wastegate valve at an associated operating condition of said internal combustion engine.
 21. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine, comprising: a. an inlet, wherein said inlet provides for receiving the flow of exhaust from the internal combustion engine; b. a wastegate valve, wherein said wastegate valve provides for dividing said flow of exhaust between first and remaining second portions, each of said first and remaining second portions of said flow of exhaust is greater than or equal to none of said flow of exhaust, and less than or equal to all of said flow of exhaust, and when commencing the operation of said turbo-compounding system, a division of said flow of exhaust is controlled so that said remaining second portion of said flow of exhaust includes all of said flow of exhaust received from said internal combustion engine that will flow through said associated open wastegate valve at said associated operating condition of said internal combustion engine; c. a bladed turbine rotor, wherein the turbo-compounding system is configured so that said first portion of said flow of exhaust impinges upon a plurality of blades of said bladed turbine rotor, and said turbo-compounding system is configured so that said remaining second portion of said flow of exhaust bypasses said plurality of blades of said bladed turbine rotor; d. a generator operatively coupled to, and driven by, said bladed turbine rotor so as to provide for generating electrical power responsive to mechanical shaft power from said bladed turbine rotor responsive to an interaction thereof with said first portion of said flow of exhaust from said internal combustion engine; and e. an induction motor, wherein an electrical input to said induction motor is operatively coupled to an electrical output of said generator, and an output shaft of said induction motor is operatively coupled to an output shaft of said internal combustion engine so as to provide for transferring said mechanical shaft power from said induction motor to said output shaft of said internal combustion engine.
 22. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 21, wherein said generator comprises a multi-phase A.C. synchronous generator, said induction motor comprises a multi-phase induction motor, the number of phases of said multi-phase induction motor is at least three and equal in number to the number of phases of said multi-phase A.C. synchronous generator, and each phase of said multi-phase induction motor is electrically associated with a corresponding phase of said multi-phase A.C. synchronous generator.
 23. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 22, wherein said generator comprises a multi-phase A.C. permanent-magnet generator.
 24. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 22, wherein a number of poles of said multi-phase A.C. synchronous generator differs from a number of poles of said multi-phase induction motor so as to provide for a substantial reduction of the rotational speed of said multi-phase induction motor relative to that of said multi-phase A.C. synchronous generator.
 25. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 22, further comprising a means for decoupling a flow of power from said generator to said internal combustion engine.
 26. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 25, further comprising: a. a first frequency or rotational speed sensor, wherein said first frequency or rotational speed sensor generates a first signal responsive to a frequency or rotational speed of said generator; b. a second frequency or rotational speed sensor, wherein said second frequency or rotational speed sensor generates a second signal responsive to a frequency or rotational speed of said induction motor; and c. a controller, wherein said controller is operatively coupled to said first and second frequency or rotational speed sensors, and to said means for decoupling said flow of power from said generator to said internal combustion engine, and said controller controls said means for decoupling said flow of power from said generator to said internal combustion engine responsive to said first and second signals.
 27. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 25, further comprising: a. a phase current sensor, wherein said phase current sensor generates a phase current signal responsive to a measurement of phase current in a conductor electrically connecting a phase of said generator to a corresponding phase of said induction motor; and b. a controller, wherein said controller is operatively coupled to said phase current sensor, and to said means for decoupling said flow of power from said generator to said internal combustion engine, and said controller controls said means for decoupling said flow of power from said generator to said internal combustion engine responsive to said phase current signal.
 28. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 22, further comprising: a. a contactor or at least one relay, wherein said contactor or said at least one relay provides for electrically connecting said generator to said induction motor when said contactor or said at least one relay is closed, and said contactor or said at least one relay provides for electrically disconnecting said generator from said induction motor when said contactor or said at least one relay is open; and b. a controller, wherein said contactor or said at least one relay is operatively coupled to said controller, and said controller provides for controlling whether said contactor or said at least one relay is either open or closed.
 29. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 22, further comprising: a. a solid-state switching or control system, wherein said solid-state switching or control system provides for electrically connecting said generator to said induction motor when said solid-state switching or control system is in a conducting state, and said solid-state switching or control system provides for electrically disconnecting said generator from said induction motor when said solid-state switching or control system is in a non-conducting state; and b. a controller, wherein said solid-state switching or control system is operatively coupled to said controller, and said controller provides for controlling whether said solid-state switching or control system provides for said generator to power said induction motor.
 30. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 22, further comprising: a. an electrically-controlled clutch coupling said output shaft of said induction motor to said output shaft of said internal combustion engine; and b. a controller, wherein said electrically-controlled clutch is operatively coupled to said controller, and said controller provides for controlling whether said electrically-controlled clutch engaged or disengaged.
 31. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 21, wherein said generator comprises a multi-phase induction generator, said induction motor comprises a multi-phase induction motor, the number of phases of said multi-phase induction motor is at least three and equal in number to the number of phases of said multi-phase induction generator, and each phase of said multi-phase induction motor is electrically associated with a corresponding phase of said multi-phase induction generator, further comprising: a. a multi-phase induction generator inverter; and b. an induction generator rotational-speed sensor, wherein said multi-phase induction generator inverter generates a multi-phase excitation signal, a frequency of said multi-phase excitation signal is responsive to a rotational-speed signal from said induction generator rotational-speed sensor, and each phase of said multi-phase excitation signal is electrically associated with a corresponding phase of said multi-phase induction generator.
 32. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 31, wherein a number of poles of said multi-phase induction generator differs from a number of poles of said multi-phase induction motor so as to provide for a substantial reduction of the rotational speed of said multi-phase induction motor relative to that of said multi-phase induction generator.
 33. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 21, further comprising a means for decoupling a flow of power from said generator to said internal combustion engine.
 34. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 33, further comprising: a. a first frequency or rotational speed sensor, wherein said first frequency or rotational speed sensor generates a first signal responsive to a frequency or rotational speed of said generator; b. a second frequency or rotational speed sensor, wherein said second frequency or rotational speed sensor generates a second signal responsive to a frequency or rotational speed of said induction motor; and c. a controller, wherein said controller is operatively coupled to said first and second frequency or rotational speed sensors, and to said means for decoupling said flow of power from said generator to said internal combustion engine, and said controller controls said means for decoupling said flow of power from said generator to said internal combustion engine responsive to said first and second signals.
 35. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 33, further comprising: a. a phase current sensor, wherein said phase current sensor generates a phase current signal responsive to a measurement of phase current in a conductor electrically connecting a phase of said generator to a corresponding phase of said induction motor; and b. a controller, wherein said controller is operatively coupled to said phase current sensor, and to said means for decoupling said flow of power from said generator to said internal combustion engine, and said controller controls said means for decoupling said flow of power from said generator to said internal combustion engine responsive to said phase current signal.
 36. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 21, further comprising: a. a contactor or at least one relay, wherein said contactor or said at least one relay provides for electrically connecting said generator to said induction motor when said contactor or said at least one relay is closed, and said contactor or said at least one relay provides for electrically disconnecting said generator from said induction motor when said contactor or said at least one relay is open; and b. a controller, wherein said contactor or said at least one relay is operatively coupled to said controller, and said controller provides for controlling whether said contactor or said at least one relay is either open or closed.
 37. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 21, further comprising: a. a solid-state switching or control system, wherein said solid-state switching or control system provides for electrically connecting said generator to said induction motor when said solid-state switching or control system is in a conducting state, and said solid-state switching or control system provides for electrically disconnecting said generator from said induction motor when said solid-state switching or control system is in a non-conducting state; and b. a controller, wherein said solid-state switching or control system is operatively coupled to said controller, and said controller provides for controlling whether said solid-state switching or control system provides for said generator to power said induction motor.
 38. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 21, further comprising: a. an electrically-controlled clutch coupling said output shaft of said induction motor to said output shaft of said internal combustion engine; and b. a controller, wherein said electrically-controlled clutch is operatively coupled to said controller, and said controller provides for controlling whether said electrically-controlled clutch engaged or disengaged.
 39. A turbo-compounding system that provides for recovering power from a flow of exhaust from an internal combustion engine as recited in claim 21, wherein when terminating the operation of recovering said power from said first portion of said flow of exhaust, said division of said flow of exhaust is controlled so that said remaining second portion of said flow of exhaust includes all of said flow of exhaust received from said internal combustion engine that will flow through an associated open wastegate valve at an associated operating condition of said internal combustion engine. 